A recent study has found that Australian marsupials such as tree possums, bandicoots and quolls are suffering a sudden decline, placing them at risk of extinction in Australia.

The northern quoll is the smallest of the four Australian quoll species

Dramatic decline

Several of Australia’s unusual marsupials, including bandicoots and phascogales, are currently experiencing a dramatic decline in the north of the country, according to recent research. Small mammal species across the continent have been known to be at risk of extinction for some time, but Chris Johnson, a wildlife conservation professor from the University of Tasmania, noted a marked and worrying change in the northern regions of Australia.

“There’s a pretty clear picture and it shows that lots of species have declined dramatically,” he said. “Where we can infer the timing of decline, it’s been fairly recent and there are now large areas where small mammals are either very rare or don’t exist but the habitat looks like it should support small mammals.”

The northern brush-tailed phascogale is classified as Vulnerable on the IUCN Red List

Worrying changes

The recent changes have been described by scientists as being a ‘new wave of decline’, but Johnson says that it is not clear how sudden these changes were. The most noticeable declines began in the early 1990s, and were particularly evident in conservation areas such as Kakadu National Park in the Northern Territory. In recent decades, around 20 small native mammal species have disappeared from Kakadu, including bandicoots, northern quolls, tree possums and northern brush-tailed phascogales, and a similar pattern has been seen in other parts of the country.

The western barred bandicoot is one marsupial which has already been lost from most of its former range in southern and western Australia

Feline culprits

Scientists analysed information from a database of current mammal populations, comparing the current wave of extinction across different species with past extinction patterns. The researchers reported their findings to a meeting of experts in Canberra this week, revealing that some common factors had emerged.

“First, the extinctions are occurring mainly in ground-dwelling animals of small body size which live in open, dry habitat. This points the finger of suspicion strongly at an introduced predator – the cat,” said Johnson. “We have seen similar extinction patterns driven by predators like foxes in southern Australia – so the big question was: ‘Is history repeating itself, or is it something new?’”

Johnson explained that the declines were being seen in species typically eaten by cats, and that, tellingly, no such declines were seen in cat-free regions. However, cats are thought to have been introduced with the settlement of Europeans in the late 1700s, while the noticeable marsupial declines were far more recent, prompting Johnson and his colleagues to ask: what had changed to make cats such a damaging predator?

Professor Johnson suggests boosting local biodiversity through the reintroduction of native predators such as the dingo

Unanswered questions

Typical factors in species decline include the outbreak of disease and habitat loss through land clearance, but neither of these was evident in northern Australia. However, it is thought that the use of fire by cattle ranchers may be having an effect on native marsupial populations.

“It is probably no one thing,” said Johnson, “but the data points to a combination of several effects – all of which tend to favour the hunting style adopted by cats which places small ground-dwelling animals at greater risk.”

The creation of sanctuaries in the bush or on offshore islands is one method currently being used to help protect a variety of marsupial species and boost their falling numbers. However, Professor Johnson is also championing a method which involves boosting local biodiversity by allowing the breeding and reintroduction of predators such as dingos to ecosystems where they have been eradicated by humans. It is hoped that, as the native predators replace feral predators or at least reduce their numbers, native prey species will be given the opportunity to rebound and thrive.